I just cant seem to break the nut lose to replace the seal,,any suggestions?

 

Air gun? maybe some careful heat?

 

Is the rear in or out of the car?

 

If the rear is in the car, just have someone stand on the brakes while you loosen it. If not, you need to make a tool to hold the pinion. A simple piece of steel bar or angle iron, with two holes to pick up two of the holes in the pinion flange, will work fine. Note that if you are simply replacing the seal and not rebuilding the center section, you need to mark the position of the nut before you remove it. When you reinstall, you need to retorque to that position, then go just a little more to avoid distorting the crush sleeve.